Computer networks are defined by their structure—bus, star, or some combination, and the organization of their bits—packets, continuous, or some combination.
Computer networks are almost always packet-based. That is because data is naturally bursty. A lot of data flows when a user opens a web page, but while he or she is reading it there is no data moving. Packets also let a number of terminals share the same wire.
In contrast, digital telephone networks are “circuit-switched”—a circuit is open for the duration of the connection. These two styles are good matches to the two data types, but there has developed a need to mix them up. If one has only a telephone line and wants to connect to the Internet, the data packets must be formatted and (usually) sent off to a modem. This works, but is inefficient because the line is held open and null data is being sent between the bursts of data that matter. If one wants to send audio over packet networks, the continuous audio data must be converted into packets and then the packets are reconverted into audio signals back together at the receiving end.
Efforts to improve this cumbersome process make sense because:                computer networks are much cheaper these days than circuit-oriented networks owing to their ubiquity and high-volume,        it is often desirable to have both audio and data simultaneously on the same network,        and computers are now very often either the source or destination for audio signals.        
One example that illustrates a convergence of the two networks styles most clearly in the VOIP (Voice Over Internet Protocol) telephone application that is rapidly gaining popularity. The idea is that only one cable is needed to connect both a PC and a telephone. The switch that makes this happen is a cheap commodity Ethernet switch rather than an expensive proprietary PBX. The cost benefit is significant.
The same reasoning applies to the high-fidelity audio networks used in radio stations and other studio facilities, with their expensive PBX-like router switches at the core. Thus, the motive to use Ethernet for audio transmission.
Original Ethernet
Originally, Ethernet networks were packet networks, but by convention, Ethernet packets are also called frames, (not to be confused with the term audio frames used later in this application). These range from 72 to 1526 bytes, depending on the amount of data to be carried. The original Ethernet was based on a single shared coaxial cable—the Ether in Ethernet's name. The very first versions used a ½″ thick cable with physical taps into it—one actually had to cut a little piece out of the jacket and screw in a metal part that made contact with the ground and center conductors. Later, the coax cable was smaller and T-connectors were used at the back of connected computers, but the principle remained the same. Even when Ethernet transitioned to telephone-style twisted-pair wires with a central hub, the medium was shared in the same way.
When a terminal was transmitting, it owned the full capacity of the cable. That means that there had to be some method to arbitrate access so that data from the various terminals didn't interfere with each other and that all had a chance to get on the bus and use a fair piece of the available bandwidth. This was done by the MAC—Media Access Controller—in each terminal. Robert Metcal invented the method at Xerox PARC in 1973. His mechanism senses when a collision occurs—collision detect. Upon detecting a collision, both data sending terminals would choose a random back-off time and then retransmit their packets with a good probability for success. The system also included a listen-before-talk function to reduce collisions—carrier sense. Using these methods, all terminals could access to the channel—multiple access. Put these all together and you understan why the Ethernat's channel access protocol is called a Carrier Sense Multiple Access with Collision Detect (CSMA/CD).
U.S. Pat. Nos. 6,161,138, 5,761,431, and 5,761,430 are assigned to Peak Audio. The technology disclosed in these patents allows audio signals to be reliably sent over the classic shared Ethernets. One of the connected terminals is set to be the “conductor” and sends a synchronizing packet onto the network that all terminals listen to. Then each terminal is assigned a timeslot on the network. The slots were offset in time with reference to the conductor's beat packet. That way, no collision or packet contention occur so that smooth audio flow is obtained. These patents describe the method of using a “beat clock” to control access to a shared network among audio terminals in a isochronous fashion so that each terminal puts its packets on the network in a prescribed time slot.
Switched Ethernet
While the marketing name has been retained and there is compatibility with the original Ethernet, modem, switched Ethernet is a fundamentally different technology. With a dedicated full-duplex connection from each terminal and a central switch that routes traffic, Ethernet is no longer a shared medium system—and therefore does not need or use a Media Access Controller and the associated CSMA/CD scheme. Network Interface Cards used with Ethernet switches automatically disable these functions.
The aforementioned three patents that are assigned to Peak Audio relate to the classic Ethernet CSMA/CD architecture with its shared medium approach and do not mention switched Ethernets. Peak Audio is presently marketing an audio networking system under the designation CobraNet which is used over switched networks and may benefit from the switched Ethernet architecture because it may provide more aggregate bandwidth and thus more audio channels are possible. However, CobraNet does not use switched Ethernet efficiently when audio and data share a link. Cobranet must route any data that shares a link with audio through their access module to ensure that it does not interfere with smooth audio flow.